There has already been proposed a power device including a tube that is characterized in that if a substance such as gas, liquid and solid, or a mixture thereof is infused into the tube, a size thereof in its longitudinal direction is restrained but it expands in its radial direction, a cylindrical sleeve that is extensible or contractible in its longitudinal direction and radial direction is disposed outside the tube, both ends of the tube are restrained, an inlet is formed in one of the ends, and a film or fiber made of polyester-based, polyamide-based, polyethylene-based, polyimide-based, polystyrene-based, polycarbonate-based substance or mixture thereof is used as the tube (patent documents 1 and 2).
Further, a motion-assisting device utilizing this kind of power device is also proposed (patent documents 3 and 4).
[Patent Document 1] Japanese Patent Application Laid-open No. 2004-105263
[Patent Document 2] Japanese Patent Application Laid-open No. S52-40378
[Patent Document 3] PCT Application Laid-open No. 2007/043308
[Patent Document 4] Japanese Patent Application Laid-open No. 2007-167484